1. Field of the Invention
The invention relates in general to a liquid crystal display and a driving method thereof, and more particularly to a color sequence liquid crystal display and a driving method thereof.
2. Description of the Related Art
With the rapidly developed image display technology, the liquid crystal display, which is thin and light weighted and has the low electromagnetic radiation, has become a mainstream display product.
A color sequence liquid crystal display sequentially displays three primary color components of one pixel to represent the color. Three light-emitting sources for respectively outputting red, green, and blue light serve as a backlight source for each pixel of this color sequence liquid crystal display. In one frame time, sub-pixels of the pixels sequentially display three sets of data, and respectively and correspondingly output the red, green, and blue light. A person can recognize the color of this pixel according to his/her persistence of vision.
However, the color sequence liquid crystal display has to feed one set of image data to the pixel in three times. So, the driving frequency of the pixel has to be increased from the original 60 Hz to 180 Hz. As for the color sequence liquid crystal display, the driving frequency of the pixel is increased to 180 Hz. That is, the driving voltage for the liquid crystal has to be updated every 5.56 milliseconds (ms). The time of 5.56 ms includes the time when the backlight module lights up, and the liquid crystal molecule has to finish the response before the backlight module lights up, so the allowable response time of the liquid crystal molecule is substantially shorter than 5.56 ms.
FIG. 1A shows a relationship between time and a transmittance of a conventional liquid crystal display panel. As shown in FIG. 1A, T1 represents a transmittance of a first pixel, and Tn represents a transmittance of an Nth pixel. The first pixel is located in a first row of pixels of the pixel array, and the Nth pixel is located in an Nth row of pixels of the pixel array. First, a corresponding pixel voltage is provided to the first pixel to make a maximum transmittance of the first pixel substantially equal a predetermined transmittance TMax. Then, a corresponding pixel voltage is provided to the Nth pixel at a time point t1 to make a maximum transmittance of the Nth pixel substantially equal the predetermined transmittance TMax. Thereafter, the backlight module is turned on between time points t2 to t3. As shown in FIG. 1A, at the time point t2 when the backlight module is turned on, the liquid crystal molecules of the Nth pixel do not respond completely. That is, the transmittance of the Nth pixel at time point t2 is substantially smaller than the predetermined transmittance TMax. The pixels in different rows receive the pixel voltages at different time points, and the pixel closer to the bottom of the panel receives the pixel voltage later, so the liquid crystal molecules thereof respond later. When the backlight module is turned on, the liquid crystal molecules on the bottom of the panel have not responded completely yet while the liquid crystal molecules on the top of the panel have responded completely, so the upper and lower portions of the liquid crystal display panel have different luminance.
FIG. 1B shows gamma curves of the liquid crystal display panel of FIG. 1A. In addition, as shown in FIG. 1B, the difference between the transmittances of the first pixel P1 and the Nth pixel Pn at the first reference gray level G1 is ΔL1, and the difference between the transmittances of the first pixel P1 and the Nth pixel Pn at the second reference gray level G2 is ΔL2. As shown in FIG. 1B, ΔL1 and ΔL2 are far greater than zero, which means that the gamma curve of the first pixel P1 are not coincide with the gamma curve of the first pixel P2, which leads to the shifting of gamma curve.
It is a subject of the panel manufacturer to improve the phenomenon of the non-uniform luminance of the liquid crystal display panel caused by the fact that the pixels in different rows are scanned and enabled in different time points, and thus to reduce the shifting of the gamma curve.